Here is how you add a new project to SCM:

1. Open XCode.
2. Go to SCM -> Repositories.
   1. Select the repository you want to import the project into.
   2. Navigate to the folder you want the project folder to be imported into.
   3. Hit the Import button.
      1. Select the folder you want imported.
      2. Hit Import.
   4. Animated Wait Icon Time!
   5. You will be notified when the import is done.

That's it.  Now tell everyone you're working with where to check out the project.  You can also now go into your project settings and set the SCM Repository to your repository so you can check in any future changes.